Which technique is more efficient for replacing duplicate records in MySQL?

To replace duplicate records and avoid any error while inserting, use INSERT ON DUPLICATE KEY UPDATE. Let us first create a table −

mysql> create table DemoTable
   -> (
   -> Id int,
   -> Name varchar(20),
   -> UNIQUE(Id,Name)
   -> );
Query OK, 0 rows affected (0.78 sec)

Insert some records in the table using insert command −

mysql> insert into DemoTable values(101,'Chris') on duplicate key update Id=10001,Name='Robert';
Query OK, 1 row affected (0.23 sec)
mysql> insert into DemoTable values(102,'Mike') on duplicate key update Id=10001,Name='Robert';
Query OK, 1 row affected (0.17 sec)
mysql> insert into DemoTable values(101,'Chris') on duplicate key update Id=10001,Name='Robert';
Query OK, 2 rows affected (0.10 sec)

Display all records from the table using select statement −

mysql> select *from DemoTable;

This will produce the following output −

+-------+--------+
|    Id | Name   |
+-------+--------+
|   102 | Mike   |
| 10001 | Robert |
+-------+--------+
2 rows in set (0.00 sec)